High voltage ignition coils have been in use in various types of applications for many years. Typically, a high voltage type transformer is fabricated by winding a primary winding on a bobbin and winding a secondary winding on a portion of the same bobbin. The winding forms or bobbins are then interlinked by magnetic members and the entire device is encased in a potting material that insulates the various potentials. This type of structure is expensive, heavy, and is erratic in its reliability due to possible voids in the potting or insulating material that is used to isolate the high voltage windings.
In recent years, a relatively new application for high voltage ignition transformers has evolved. This application is the use of a high voltage spark ignition type transformer as a spark ignition source for fuel gas in fuel burners, such as gas furnaces. The need for ignition sources in this type of an environment has been dictated by an increase in cost of fuel, and by legislation. The past practice in fuel ignition systems for furnaces has been to rely on a standing pilot flame that is monitored by a thermocouple or similar safety device as the ignition source for the main burner. This type of standing pilot configuration is very reliable and inexpensive to construct, but this structure utilizes fuel gas constantly. As such, the use of gas is considered inappropriate due to the shortage of gas and its accelerating cost. This pair of factors has lead to the legislation of standing pilot configurations out of existence in many states. To replace the standing pilot, a number of fuel burner or furnace manufacturers have begun to rely on a spark ignition system that provides an ignition spark at a pilot burner to ignite the pilot burner. The pilot burner is then monitored by a flame rod or other technique to ensure that the pilot flame exists. That pilot flame is then used to ignite a main burner. This type of equipment must be reliable, it must be inexpensive, and it must be small. The present state of the art utilizes a high voltage ignition transformer, and these transformers have been more expensive and less reliable than is desirable.